Flickr is amazing. It's great for photo hosting, that's why I signed on with them in the first place. But since then, I've developed a number of contacts through Flickr; people that like my photos, or are into whatever I posted on the site. I have a contact from Barcelona, a few local friends I've never met, and somebody from Boston who seems really neat but I have never spoken to.
Flickr also has groups, which are fun. I stumbled into groups when I got an email out of the blue to post some photos I had taken of Fatbacks (titanium "Pugsley" -like bikes from Anchorage) on the Flickr group "Titanium Bike Addict". That was the gateway - after that I got into the Surly Pugsley group, then the Xtracycely group, and then "Things I see in my neighborhood".
My latest favorite is "Stick Figures in Peril". It's simply a collection of safety signs showing stick figures in precarious situations. I made my first contribution last night - it is a photo of a Tsunami safety magnet we got when we lived in Anchorage. Some really funny stuff here. It makes me glad I am not a stick figure after seeing some of the bad shit they get into.